Problem: Solve for $r$ : $-17 + r = 18$
Solution: Add $17$ to both sides: $ \begin{eqnarray} \\ -17 + r &=& 18 \\ \\ {+17} && {+17} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-17 + r} &\hphantom{=}& \hphantom{18} \\ r &=& 18 {+ 17} \\ \end{eqnarray} $ Simplify. $ r = 35$